Obama To Tell Iran That U.S. Will 'Do What We Must' On Nukes

"President Barack Obama will warn Iran on Tuesday that the United States will 'do what we must' to prevent it from acquiring a nuclear weapon, and appeal to world leaders for a united front against further attacks on U.S. diplomatic missions in Muslim countries," Reuters reports this morning.

Update at 8:30 a.m. ET. According to excerpts released by the White House, the president will say:

"America wants to resolve this issue through diplomacy, and we believe that there is still time and space to do so. But that time is not unlimited. We respect the right of nations to access peaceful nuclear power, but one of the purposes of the United Nations is to see that we harness that power for peace. Make no mistake: a nuclear-armed Iran is not a challenge that can be contained. It would threaten the elimination of Israel, the security of Gulf nations, and the stability of the global economy. It risks triggering a nuclear-arms race in the region, and the unraveling of the non-proliferation treaty. That is why a coalition of countries is holding the Iranian government accountable. And that is why the United States will do what we must to prevent Iran from obtaining a nuclear weapon."

USA Today's The Oval blog adds that Obama will also "pay tribute to Ambassador Chris Stevens in his address." Stevens died after a Sept. 11 attack on the U.S. consulate in Benghazi, Libya.

The president is scheduled to be among the first from a long list of world leaders addressing the annual opening of the United Nations General Assembly this week. He's due to speak just after 10 a.m. ET. The U.N. webcasts its proceedings here. We will be posting updates as the president and other leaders address the assembly.

"Were there any doubt that the U.S. presidential campaign hung heavy over Obama's speech to the General Assembly, Republican rival Mitt Romney shredded it by assailing Obama's foreign affairs leadership on the eve of the president's speech.

" 'This is time for a president who will shape events in the Middle East, not just be merciful or be at the mercy of the events,' Romney said Monday. Focusing on the killing of the U.S. ambassador in Libya and mass bloodshed in Syria, Romney repeatedly ridiculed Obama's comment that nations moving toward democracy after the Arab Spring face 'bumps in the road.' "

Both Obama and Romney are scheduled to address the Clinton Global Initiative today.

On Morning Edition today, NPR's Michele Kelemen previewed the "busy week of diplomacy" for Obama and Secretary of State Hillary Rodham Clinton. And she noted that among the other leaders who will be speaking are Iranian President Mahmoud Ahmadinejad, on Wednesday, and Israeli Prime Minister Benjamin Netanyahu, on Thursday.